This invention relates to process sensors and is more particularly concerned with process sensors for use with electrically non-conducting lined steel vessels.
Glass lined steel vessels, for example, are widely used to process products in the chemical, food and beverage industries. The glass lining is relatively inert to acids while the steel vessel has the strength to withstand pressure and temperature extremes.
The lining is, under some circumstances, subject to corrosion or wear. This is undesirable as an interaction of the product and the steel could cause the steel to corrode, contaminating the product and affecting the integrity of the tank. Periodic visual inspection of the tank is recommended, but faults may be as small as pin holes and pass unnoticed. For this reason, electric fault finders have been developed which can continually monitor the tank for any fault which may be in the lining.
One type of fault finder uses the conductivity of the product to provide a reading. An electrode is immersed in the product and an electric potential is maintained between the electrode and the steel portion of the vessel. If there is a fault, the product will make contact with the steel and complete an electric circuit.
A second type of fault finder uses the electrolytic property of the product. A non-steel electrode is immersed in the product. If the product makes contact with the vessel steel a galvanic reaction occurs and an electric cell is then formed with the exposed steel as a second electrode. The voltage across the non-steel electrode and steel vessel body will give an indication of the condition of the lining. This invention is an improvement of this type of galvanic fault finder, while also providing means to measure temperature of the product.